Stockholders' Equity - Employee Stock Options (Details) - Stock Options [Member] - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected term in years	4 years 4 months 24 days	4 years 4 months 24 days
Volatility	33.50%	34.20%
Risk-free interest rate	1.30%	2.50%
Dividend rate	0.00%	0.00%
Number of Shares
Balance - Beginning (in shares)	2.7
Granted (in shares)	0.5
Forfeited (in shares)	0.0
Exercised (in shares)	(0.2)
Balance - Ending (in shares)	3.0
Weighted- Average Exercise Price
Balance - Beginning (in dollars per share)	$ 50.37
Granted (in dollars per share)	114.48
Forfeited (in dollars per share)	59.28
Exercised (in dollars per share)	40.02
Balance - Ending (in dollars per share)	$ 62.41
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options vested and expected to vest, Outstanding (in shares)	3.0
Options vested and expected to vest, Weighted average exercise price (in dollars per share)	$ 62.41
Options vested and expected to vest, Weighted average remaining contractual life (in years)	4 years 9 months 18 days
Options vested and expected to vest, Aggregate intrinsic value	$ 123.8
Options exercisable, Outstanding (in shares)	1.5
Options exercisable, Weighted average exercise price (in dollars per share)	$ 39.50
Options exercisable, Weighted average remaining contractual life (in years)	3 years 6 months
Options exercisable, Aggregate intrinsic value	$ 90.3
Compensation cost not yet recognized	$ 38.6
Compensation cost not yet recognized period of recognition	3 years 1 month 6 days
Weighted-average fair value per share granted	$ 33.82	$ 27.12
Intrinsic value of options exercised	$ 13.1	$ 27.2
Fair value of options vested	$ 6.0	$ 4.2